Making twisted multifilament yarn



July 4, 1944. J. E. PIERCE 2,352,861

MAKING TWISTED MUL'lI-FILAMENT YARN Filed June 19, 1941 Patented its 4, i944 um'rso STAT-BS PATENT OFFICE 1 v I attend emf i-Tfiffe z. Mich... :3;

meme assignments, to The Visking omratlon. Chicago, 111., a corporation of Illinois Application June 19, 1941, Serial No. 398,696

" (oils-is) SOlalma.

This invention relates to a method of producing a multi-strand yarn, cord, or rope from a plurality of filaments of a normally crystalline poly-.

merso as to impart thereto, or impose thereon, a permanent twist.

There has recently been made available a group of synthetic plastic materials which, in contrast to those previously known and commonly em-' ployed, are crystalline when examined by X-ray diffraction methods. These crystalllne'polymers include, among others, the polymer of vinylidene chloride 'alone and many of its co-polymers with other polymerizable compounds, wherein the vlnylidene chloride predominates. Such polymers have been shown to be capable of forming especially strong filaments when heated to a fusion temperature suificient to cause disappearance of the crystalline structure. formed into filaments suitably by extrusion, and chilled to congeal the polymer and to produce a temporarily int drawn to form strong filaments oriented along the fiber axis, are herein referred to for convenience as normally crystalline-polymers."

Those containing vinylidene chloride are here called normally crystalline vinylidene chloride polymers.

it has been found that when a; plurality of l filaments, prepared as above-described from a normally crystalline polymer, are twisted together in attempt to form a yarn, cord, rope, or similar twisted multi-stra'nd article, the twist is not permanent, since the individual strands have already been deformed plastically to the limit of which they are capable, and the accompanying crystallization h'as imparted to them a permanent set. .Yarns s'o-prepared tend to unwind, leaving a loose bundle of parallel strands. It has been found further that when attempts are made-to twist together a plurality of filaments of 'normally crystalline polymers whilethey are still hot and substantially non-crystalline, just as they emergefrom the extrusion orifices, they tend to fuse togethen Another disadvantage of suchoperation has been found to be that when .the strands are twisted hot a considerable variation in denier is imparted to the individual subsequent stretching operation intended to resuit in orientation. If the strands are'twisted.

together while hot and then simply allowed to stand until crystallization occurs, no advantage in strength is obtained over similarly twisted strands of the usual amorphous plastics.

It is a primary object of this invention to provide a particular method whereby twisted multistrand yarn, cord, rope, or similar article of cordage may be prepared from a plurality of filaments of a normally crystalline polymer in such manner that a permanent set is imparted to each individual strand, and the twisted assembly has no tendency to untwist. A particular object is to provide a method as aforesaid, applicable to the normally crystalline polymers of vinylidene chloride. Related objects will become apparent from the following description.

The inventionis set forth in the following description, with the aid of the accompanying drawn ing, the single figure of which is a diagrammatic representation of an apparatus wherein the invention may be carried out.

.The method of the invention, comprises the steps of providing a plurality of strands of a' and its mode of operation may be explained with I reference to the accompanying diagram. A

normally crystalline polymer is heated to a ing bath H, which is at a temperature willciently low to convert the hot plastic polymer to the cold "supercooled form. From bath M the strands are passed several times around snu'bbing rolls l5 and I6, which are cocked at a slight axial angle to one another to cause successive turns of the filaments to be displaced laterally, making room for the oncoming filaments from the supercooling bath it. The

strands either during twisting or during any strands arepassedas a cluster ll through g ther may be associated with driving means 23 through a friction plate II or other slip clutch.

The invention may be illustrated specifically with respect to operations carried out on a normally crystalline co-polymer of vinylidene chloride and vinyl chloride, about 90 per cent of the former and about per cent of the latter. The polymer is heated to about 195 C. in the chamber of an extrusion press 10 and is extruded through a die having five openings 0.032 inch in diameter, to form five filaments simultaneously. Operation is continuous, and the five filaments are supercooled while being conducted through a bath M of chilled water or' other liquid, such as miscible oil, at about 3 C. The peripheral speed of snubbing rollers l5 and I6 is adjusted so that the hot filaments I I are drawn down to a diameter of about 0.016 inch at the point where they enter bath l4 and are congealed. Such hot stretching does not result in any appreciable crystallization of the polymer in the filaments. The snubbing rolls serve to prevent transmission of tension, additional to that required for drawing the hot filaments as above stated, applied beyond those rolls back to the zone near the extrusion orifices where the filaments are hot and easily deformed. After a supply of supercooled filaments has been gathered through eye l8 and fed onto bobbin 20, the bobbin is set in motion, as through drive belt 23, by means not shown. The rate of rotation of bobbin is adjusted to effect substantially all stretching of which the supercooled filaments in cluster I! are capable, without rupture, which is always over 200 per cent of their supercooled length,

and usually is from 300 to about 400 per cent of that length. This effects a crystallization of the polymer in the strands of yarn l9 and a reduction in diameter of the individual strands to from 0.7 to 0.5 their supercooled diameter. Thus, each filament which was originally 0.016 inch in diameter when first supercooled, may now be from 0.011 inch to 0.008 inch in diameter and all filaments in the yarn i9 will be of the same diameter. The balloon spinning, created by the cap twister, twists the five strands together while they are being stretched by the speed of the bobbin, so that the permanently set shape resulting from the crystallization caused by stretching is a twisted shape, each filament being set permanently in its proper position in the multi-strand yarn.

It is preferred that no stretching be done in the supercooling bath H, so that maximum strength may be obtained in the subsequently twisted and crystallized multi-strand article. Any stretching between the extrusion orifice and the point at which twisting is initiated should be confined to the hot filaments H emerging from the extrusion orifice. This is easily controlled by keeping the temperature of bath l4 sufficiently low to ensure congelation of the strands it promptly after immersion in bath M. It must be remembered that stretching at this point is only for the purpose of reducing the diameter of the filaments to a diameter of from about 1.4 to about 2 times that desired in the final, fully stretched and twisted, individual filaments going to make up the finished yarn.

The number of filaments employed in making the multistrand article is a matter of choice as and convenience, and may vary from 2 to 20 or more. The amount of twist imparted in the yam-forming operation varies with the diameter of the individual strands and the type of article desired, but it has been found that at least 2 full twists per linear inch are necessary to ensure obtaining a permanent set when the individual strands are between 0.002 and 0.10 inch in diameter. Individual strand diameters may vary widely from 0.0005 inch or less to 0.1 inch, but for many uses, final diameters of 0.004 to 0.08 inch are preferred.

In a specific example, when operating on the vinylidene chloride-vinyl chloride co-polymer above described, four filaments were extruded at C. through orifices .080 inch in diameter, and stretched while hot to 0.040 inch diameter. They were chilled to 3 C. and fed to a cap twister as above-described. The bobbin had a diameter of 1.50 inch, when empty, and rotated at about 1750 R. P. M., taking up about 40 linear feet of twisted yarn per minute. The snubber I trusion rate of the original'.080 inch hot filaments was equivalent to about 2 feet per minute. The individual filaments in the finished yarn were 0.020 inch in diameter, and the yarn, which had 3.4 full twists per inch, was permanently twisted, and did not tend to come untwisted.

When high speed operation is contemplated. it is generally desirable to extrude a rather large diameter filament, drawing it down rapidly while hot to about twice its intended final diameter, and then, after supercooling it, subjecting it to the combined twisting and stretching operation. It is clear that many variations are possible in the initial and final linear speeds of the strands involved, selection being made in each instance on the basis of the equipment available, the desired ratio of stretched length to supercooled length (within the operative limits for the particular polymer), and other related factors.

It is of course to be understood that the individual strands being twisted together need not be continuous, and that known devices may be employed, along with the twisting and stretching mechanism, to convert the continuous supply of polymeric filament into staple fiber lengths for the fabrication of permanently twisted woolly yarn.

The invention is not limited to the fabrication of thread or yarn, as these terms are usually understood, but is applicable as well to the manufacture, by a concurrent stretching and twisting of supercooled strands of normally crystalline polymers, of twine, rope, and numerous other items of cordage where multi-strand twisted structure is of advantage. Neither is the invention limited to the particular co-polymer named in the foregoing description, it being generally applicable to normally crystalline polymers, many of which are now known, including a variety of polymeric substances containing a preponderance of vinylidene chloride. It is contemplated that the normally crystalline polymer employed may be modified by the inclusion in the composition of coloring agents, plasticizers, fillers, or other modifiers in such proportion that they do not appreciably affect the characteristic behavior of the crystalline polymer. While the convenience and controllability of the cap twister type of balloon spinner, with its efficient level-wind feature, has been found very desirable as a means of carrying out the invention, it is not intended that the invention be limited thereto, as will be evident from the following claims.

I claim:

1. The method which comprises providing a plurality of supercooled strands of a normally crystalline vinylidene chloride po ymer, gathering the strands into a cluster, and twisting the cluster while stretching it to efiect crystallization, thereby to form a multi-strand crystalline vinylidene chloride article with a permanent set.

2. The method which comprises providing a plurality of supercooled strands of a normally crystalline vinylidene chloride polymer, gathering the strands into a cluster, and twisting the cluster while stretching it at least 200 per cent, but short of the breaking point, to eflect crystallization and to impart at least two full twists per linear inch, thereby to form a multi-strand twis'ted crystallin vinylidene chloride article with a permanent set.

3. The method which comprises providing a plurality of filaments of the hot and now substantially non-crystauine polymer, elongating the hot filaments to a diameter of from about 1.4 to about 2 times that desired in the individual strands within the finished article, rapidly chilling the filaments to supercool them, gathering the supercooled filaments into a cluster, and twisting the cluster while stretching it to from 200 to about 400 per cent of its supercooled length, to effect crystallizati'on and to impart at least two full twists p'er linear inch, thereby to form a multi-strand twisted crystalline polymeric article of cordage with a permanent set. 1

5. The method which comprises heating a normally crystalline vinylidene chloride polymer to.

a fusion temperature, extruding simultaneously a plurality of filaments of the hot and now substantially non-crystalline polymer, elongating the plurality of supercooled strands of a normally hot filaments to a diameter of from about 1.4.

to about 2 times that desired in the individual strands within the finished article, rapidly chilling the filaments to supercool them,,gathering the supercooled filaments into a cluster, balloon-spinning the so-gathered strands at a speed to stretch them to from 200 to 400 per cent of their supercooled length to efiect crystallization and to impart at least two full twists per linear inch, thereby to form a multi-strand twisted crystalline polymeric article of cordage with a permanent set.

JAMES E. PIliiRCE. 

